The response of platelets to stimuli will be studied to determine what mechanisms couple specific stimuli to the varied responses and the sequence of events involved. Emphasis will be on secretion, a morphological response, and activation of phosphorylase, a metabolic response. Time-courses for these responses will be compared and drugs will be used to modify the response to stimuli. Stimulation by thrombin will be compared to stimulation by other agents, such as collagen, epinephrin, ADP and latex particles, in an attempt to map the sequence of events in stimulus-response coupling. The mechanisms involved will be studied by correlating functional biochemical and morphological studies, especially with respect to calcium and microtubules.